Regulation of gene expression through aptamer-modulated polyadenylation

ABSTRACT

The invention provides polynucleotide constructs for the regulation of gene expression by aptamer-based modulation of U1 small nuclear ribonucleoprotein (snRNP)-mediated suppression of polyadenylation and methods of using the constructs to regulate gene expression in response to the presence or absence of a ligand that binds the aptamer. The polynucleotide construct contains a U1 binding site in the context of a riboswitch comprising an effector region and an aptamer such that when the aptamer binds a ligand, target gene expression occurs.

FIELD OF THE INVENTION

The invention provides polynucleotide constructs for the regulation ofgene expression by aptamer-based modulation of U1 snRNP-mediatedsuppression of polyadenylation and methods of using the constructs toregulate gene expression in response to the presence or absence of aligand that binds the aptamer. The polynucleotide construct contains aU1 binding site in the context of a riboswitch comprising an effectorregion and an aptamer such that when the aptamer binds a ligand, targetgene expression occurs.

BACKGROUND OF THE INVENTION

Messenger RNAs (mRNAs) in eukaryotic cells are produced from pre-mRNAtranscripts by extensive post-transcriptional processing, including 5′end capping, removal of introns by splicing, and 3′ end cleavage andpolyadenylation. Splicing is performed by a spliceosome, a largeRNA-protein complex comprised predominantly of small nuclearribonucleoproteins (snRNPs). The predominant (U2-type) spliceosomecontains the U1, U2, U4, U6 and U5 snRNPs, whereas a much less abundantU12-type spliceosome is comprised of U11, U12, U4atac, U6atac and U5snRNPs.

The 3′ end of almost all eukaryotic mRNAs comprises a poly(A) tail—ahomopolymer of 20 to 250 adenosine residues. The poly(A) tail is addedto pre-mRNA in the nucleus by cleavage and polyadenylation, a processcatalyzed by a large complex of proteins. In vertebrates, addition of apoly(A) tail depends on two cis-acting RNA elements, the highlyconserved AAUAAA polyadenylation sequence found upstream of thepolyadenylation site and a poorly conserved GU-rich element founddownstream. Addition of a poly(A) tail to mRNA protects it fromdegradation, among other functions.

The U1 snRNP has been shown to have splicing-independent function inpre-mRNA processing by suppressing 3′ end processing of pre-mRNA,inhibiting aberrant intronic polyadenylation signal, and ensure promoterdirectionality For example, Fortes et al. (PNAS, 100:8264-69,incorporated herein by reference), placed one to three U1 binding sitesin the 3′ UTR leading to reduced reporter gene expression.

SUMMARY OF THE INVENTION

In one aspect, the present invention provides a polynucleotide cassettefor the regulation of the expression of a target gene comprising ariboswitch wherein the riboswitch comprises an effector region and anaptamer, wherein the effector region comprises a U1 snRNP binding siteand sequence complementary to the U1 snRNP binding site. In oneembodiment, the aptamer binds a small molecule ligand.

In one embodiment, the effector sequence comprises, in addition to theU1 snRNP binding site and sequence complementary to the U1 snRNPbinding, additional sequence that is capable of forming a stem when theaptamer binds ligand. In one embodiment, the effector region comprises astem-forming sequence that is 9 to 11 base pairs. In one embodiment, theeffector region comprises a stem-forming sequence with one or moremismatched bases in the stem.

In one embodiment, the U1 snRNP binding site is 8 to 10 nucleotides. Inone embodiment, the U1 snRNP binding site comprises the sequenceCAGGTAAG. In one embodiment, the U1 snRNP binding site is selected fromthe group consisting of CAGGTAAGTA, CAGGTAAGT, and CAGGTAAG.

In one embodiment, the polynucleotide cassette comprises two or moreriboswitches, wherein each riboswitch comprises an effector region andan aptamer, wherein the effector region comprises a U1 snRNP bindingsite and sequence complementary to the U1 snRNP binding site. In oneembodiment, the two or more riboswitches each comprise an aptamer thatbinds the same ligand. In one embodiment, the two or more riboswitchescomprise different aptamers that bind different ligands.

In another aspect, the present invention provides a method of modulatingthe expression of a target gene comprising:

(a) inserting one or more of the polynucleotide cassettes describedabove into the 3′ UTR of a target gene,

(b) introducing the target gene comprising the polynucleotide cassetteinto a cell, and

(c) exposing the cell to a ligand that specifically binds the aptamer inan amount effective to increase expression of the target gene.

In one embodiment, the ligand is a small molecule.

In one embodiment, the polynucleotide cassette is inserted about 87and/or about 140 nucleotides 5′ of the polyadenylation signal. In oneembodiment, the polynucleotide cassette is inserted at one or more ofabout 74, about 110, or about 149 nucleotides 5′ of the polyadenylationsignal.

In one embodiment, two or more of the polynucleotide cassettes areinserted into the 3′ UTR of the target gene. In one embodiment, the twoor more polynucleotide cassettes comprise different aptamers thatspecifically bind to different small molecule ligands. In oneembodiment, the two or more polynucleotide cassettes comprise the sameaptamer. In one embodiment, the two or more polynucleotide cassettes areinserted at different locations of the 3′ UTR of the target gene.

In another aspect, the present invention provides a target genecomprising a polynucleotide cassette described above incorporated in avector for the expression of the target gene. In one embodiment, thevector is a viral vector. In one embodiment, the viral vector isselected from the group consisting of adenoviral vector,adeno-associated virus vector, and lentiviral vector.

In another aspect, the present invention provides a vector comprising atarget gene that contains a polynucleotide cassette described herein. Inone embodiment, the vector is a viral vector. In one embodiment, theviral vector is selected from the group consisting of adenoviral vector,adeno-associated virus vector, and lentiviral vector.

BRIEF DESCRIPTION OF THE FIGURES

FIGS. 1a -1 b. U1 binding site in 3′ UTR suppresses target gene(luciferase) expression.

FIG. 1 a. Schematics for the insertion of U1 binding sequence in 3′ UTRat different position in pRL-SV40 vector. The wild type and mutant U1consensus binding sequences are listed.

FIG. 1 b. Results of Renilla luciferase assay. HEK 293 cells weretransfected with the indicated constructs containing at variouspositions in the 3′ UTR either the consensus U1 binding sequence or themutant sequence. The results were expressed as mean±SD (n=3), and thereduction fold was calculated as ratio of luciferase activity frommutant construct to luciferase activity from wild type construct.

FIGS. 2a -2 b. Effect of the length of the U1 binding sequence in the 3′UTR on suppression of gene expression.

FIG. 2a . The full length and the truncated sequences of U1 bindingsites inserted at -87 position in 3′ UTR.

FIG. 2b . HEK 293 cells were transfected with the indicated constructscontaining full length or truncated U1 binding sequences inserted at -87and luciferase activity was determined.

FIGS. 3a -3 b. The effect of stem-loop structure at the U1 site in 3′UTR on gene expression.

FIG. 3a . The sequence of the stem-loop structure that embedded the U1binding site in the stem. Mutations were made to generate a broken stem(shown on right).

FIG. 3b . Results of luciferase activity assay indicate that thestem-loop structure sequestering the U1 binding site completelyabolished the suppressive effect of U1 interference on gene expression.

FIGS. 4a -4 c. Use of a theophylline aptamer to regulate U1 interferencein 3′ UTR of a target gene.

FIG. 4a . The schematics showing the aptamer-modulated U1 interferencein 3′ UTR and gene expression. In the absence of aptamer ligand (toppanel), a U1 site inserted in the 3′ UTR is available for U1 snRNPbinding and U1-mediated polyadenylation interference, thus suppressingtarget gene expression. In the presence of aptamer ligand (lower panel),aptamer/ligand binding leads to the formation of stem which sequestersthe U1 binding site from U1 snRNP binding. U1-mediated polyadenylationinterference is abolished, resulting in target gene expression.

FIG. 4b . The sequence of the effector region stem that sequesters theU1 binding site and connects the theophylline aptamer, generated byserial truncation of the hairpin stem and lower stem of theophyllineaptamer. Shown are the stem sequences for constructs U1 theo_1, 8 and 9.Theophylline is shown as ▴.

FIG. 4c . HEK 293 cells were transfected with the indicated constructs,and treated with or without 3 mM theophylline. The induction fold wascalculated as the ratio of the value of luciferase activity obtainedfrom theophylline treated cells to the luciferase activity obtained fromuntreated cells.

FIGS. 5a -5 c. Optimization of effector region stem sequence to enhancethe regulatability of U1 site accessibility.

FIG. 5a . The stem sequences of U1_theo_8 and U1_theo_9, with thesequential mutations listed beside corresponding nucleotides. Thesequential mutations create a mismatch in the effector region stem.

FIG. 5b . A total of 9 constructs were generated through sequentialmutation of U1_theo_8 and were each transfected into HEK 293 cells.Transfected cells were treated with or without 3 mM theophylline andluciferase activity measured. The results were expressed as mean±SD, andthe induction fold was indicated for construct U1_theo_8 to U185.

FIG. 5c . A total of 8 constructs were generated through sequentialmutation of U1_theo_9 and were each transfected into HEK 293 cells.Transfected cells were treated with or without 3 mM theophylline andluciferase activity measured. The results were expressed as mean±SD.

FIGS. 6a -6 b. Effect of multiple U1_theo riboswitches in the 3′ UTR onregulation of target gene expression.

FIG. 6a . A schematic showing the 4 copies of U1_theo_8_1 in the 3′ UTRof the target gene (luciferase).

FIG. 6b . HEK 293 were transfected with the indicated constructs, andtreated with theophylline at different concentrations. Four copies ofU1_theo_8_1 in the 3′ UTR yielded a 4.3-fold induction of luciferaseactivity at 6 mM concentration.

FIGS. 7a -7 c. Use of guanine aptamer to modulate U1 interference.

FIG. 7a . Schematic indicating the U1_Gua sequence at different positionin 3′ UTR containing SV40 early poly(A) signal.

FIG. 7b . Schematic showing the effector region stem sequence in U1_Guaswitch that sequesters the U1 site (in the presence of guanine ligand)and connects guanine aptamer. Guanine is shown as ●.

FIG. 7c . Guanine aptamer regulates U1 interference with polyadenylationin response to guanine treatment. HEK 293 cells were transfected withthe indicated constructs. Constructs containing the mutant U1 site andits complementary sequence were used as control. Results were expressedas mean±SD, the induction folds are shown for each construct.

FIG. 8. U1_Gua riboswitch functions in the context of human beta globinpolyA sequence.

DETAILED DESCRIPTION OF THE INVENTION

The invention provides polynucleotide constructs for the regulation ofgene expression by aptamer-based modulation of U1 snRNP-mediatedsuppression of polyadenylation and methods of using the constructs toregulate gene expression in response to the presence or absence of aligand that binds the aptamer. The polynucleotide construct contains atleast one riboswitch that contains an effector region and a sensorregion. The effector region contains a U1 snRNP binding site andsequence complementary to the U1 snRNP binding site such that the twosequences are capable of forming a stem that sequesters the U1 snRNPbinding site thereby preventing binding of the U1 snRNP. The effectorregion may contain additional sequence and its complement so that theeffector region stem is longer than the U1 snRNP binding site and itscomplementary sequence. The sensor region comprises an RNA sequence thatbinds a ligand, and in response to this binding alters the conformationof the effector region. In one embodiment, the sensor region comprisesan aptamer. When the aptamer ligand is not present, the effector regiondoes not form a stem. The U1 snRNP binding site is available and isbound by a U1 snRNP, which inhibits polyadenylation of the mRNA. Whenthe aptamer ligand is present, it binds the aptamer causing the effectorregion to form a stem, which prevents U1 snRNP from binding the U1binding site. The U1 snRNP is not recruited to the 3′ UTR of the targetgene mRNA and polyadenylation of the message occurs.

The gene regulation polynucleotide cassette refers to a recombinant DNAconstruct that, when incorporated into the DNA of a target gene in the3′ UTR, provides the ability to regulate expression of the target geneby aptamer/ligand mediated suppression of polyadenylation by U1 snRNP.As used herein, a polynucleotide cassette or construct is a nucleic acid(e.g., DNA or RNA) comprising elements derived from different sources(e.g., different organisms, different genes from the same organism, andthe like). The polynucleotide cassette comprises a riboswitch. Theriboswitch in the context of the present invention contains a sensorregion (e.g., an aptamer) and an effector region that together areresponsible for sensing the presence of a ligand that binds the sensorregion and altering the conformation of the effector region thatcontains a U1 snRNP binding site and sequence that is complementary tothe U1 snRNP binding site. In one embodiment, the target gene'sexpression is increased when the aptamer ligand is present and decreasedwhen the ligand is absent.

Riboswitch

The term “riboswitch” as used herein refers to a regulatory segment of aRNA polynucleotide. A riboswitch in the context of the present inventioncontains a sensor region (e.g., an aptamer) and an effector region thattogether are responsible for sensing the presence of a ligand (e.g., asmall molecule) and modulating the accessibility of a U1 snRNP bindingsite located in the effector region. In one embodiment, the riboswitchis recombinant, utilizing polynucleotides from two or more sources. Theterm “synthetic” as used herein in the context of a riboswitch refers toa riboswitch that is not naturally occurring. In one embodiment, thesensor and effector regions are joined by a polynucleotide linker. Inone embodiment, the polynucleotide linker forms a RNA stem (i.e., aregion of the RNA polynucleotide that is double-stranded).

Effector Region

The effector region of the riboswitch comprises RNA sequence that, inresponse to ligand binding the sensor region (e.g., an aptamer), forms astem structure (a double-stranded region) that lowers the accessibilityof a U1 snRNP binding site to the U1 snRNP. The effector regioncomprises a U1 snRNP binding site and sequence complimentary the U1snRNP binding site. When the aptamer binds its ligand, the effectorregion forms a stem and thus sequesters the U1 snRNP binding site frombinding a U1 snRNP. Under certain conditions (for example, when theaptamer is not bound to its ligand), the effector region is in a contextthat provides access to the U1 snRNP binding site, allowing U1 snRNP tobind the mRNA and inhibit polyadenylation leading to degradation of themessage.

The U1 snRNP binding site can be any polynucleotide sequence that iscapable of binding the U1 snRNP, thereby recruiting the U1 snRNP to the3′ UTR of a target gene and suppressing polyadenylation of the targetgene message. In one embodiment, the U1 snRNP binding site (alsoreferred to herein as the “U1 binding site” or “U1 site”) is theconsensus site CAGGTAAGTA (CAGGUAAGUA when in the mRNA). In someembodiments, the U1 snRNP binding site is a variation of this consensussequence, including for example sequences that are shorter or have oneor more nucleotides changed from the consensus sequence. In oneembodiment, the U1 snRNP binding site contains the sequence CAGGTAAG. Insome embodiments, the binding site is encoded by the sequence selectedfrom CAGGTAAGTA, CAGGTAAGT, and CAGGTAAG. The U1 snRNP binding site canbe any 5′ splice site from a gene, e.g., the 5′ splice site from humanMIER exon 2 (see Examples 7 and 8).

The stem portion of the effector region should be of a sufficient length(and GC content) to inhibit U1 snRNP binding the U1 snRNP binding siteupon ligand binding the aptamer, while also allowing access to the U1snRNP binding site when the ligand is not present in sufficientquantities. In embodiments of the invention, the stem portion of theeffector region comprises stem sequence in addition to U1 snRNP bindingsite and its complementary sequence. In embodiments of the invention,this additional stem sequence comprises sequence from the aptamer stem.The length and sequence of the stem portion can be modified using knowntechniques in order to identify stems that allow acceptable backgroundexpression of the target gene when no ligand is present and acceptableexpression levels of the target gene when the ligand is present. If thestem is, for example, too long it may hide access to the U1 snRNPbinding site in the presence or absence of ligand. If the stem is tooshort, it may not form a stable stem capable of sequestering the U1snRNP binding site, in which case U1 snRNP will bind and inhibitpolyadenylation of the message (leading to degradation of the targetgene mRNA) in the presence or absence of ligand. In one embodiment, thetotal length of the effector region stem is between about 7 base pairsto about 20 base pairs. In some embodiments, the length of the stem isbetween about 8 base pairs to about 11 base pairs. In some embodiments,the length of the stem is 8 base pairs to 11 base pairs. In addition tothe length of the stem, the GC base pair content of the stem can bealtered to modify the stability of the stem.

In some embodiments, the effector region stem contains one or moremismatched nucleotides that do not base pair with the complementaryportion of the effector region stem.

Aptamer/Ligand

In one embodiment, the sensor region comprises an aptamer. The term“aptamer” as used herein refers to an RNA polynucleotide thatspecifically binds to a ligand. The term “ligand” refers to a moleculethat is specifically bound by an aptamer. In one embodiment, the ligandis a low molecular weight (less than about 1,000 Daltons) moleculeincluding, for example, lipids, monosaccharides, second messengers,co-factors, metal ions, other natural products and metabolites, nucleicacids, as well as most therapeutic drugs. In one embodiment, the ligandis a polynucleotide with two or more nucleotide bases.

In one embodiment, the ligand is selected from the group consisting of8-azaguanine, adenosine 5′-monophosphate monohydrate, amphotericin B,avermectin B1, azathioprine, chlormadinone acetate, mercaptopurine,moricizine hydrochloride, N6-methyladenosine, nadide, progesterone,promazine hydrochloride, pyrvinium pamoate, sulfaguanidine, testosteronepropionate, thioguanosine, tyloxapol and vorinostat.

Aptamer ligands can also be cell endogenous components that increasesignificantly under specific physiological/pathological conditions, suchas oncogenic transformation—these may include second messenger moleculessuch as GTP or GDP, calcium; fatty acids, or fatty acids that areincorrectly metabolized such as 13-HODE in breast cancer (Flaherty, J Tet al., Plos One, Vol. 8, e63076, 2013, incorporated herein byreference); amino acids or amino acid metabolites; metabolites in theglycolysis pathway that usually have higher levels in cancer cells or innormal cells in metabolic diseases; and cancer-associated molecules suchas Ras or mutant Ras protein, mutant EGFR in lung cancer,indoleamine-2,3-dioxygenase (IDO) in many types of cancers. Endogenousligands include progesterone metabolites in breast cancer as disclosedby J P Wiebe (Endocrine-Related Cancer (2006) 13:717-738, incorporatedherein by reference). Endogenous ligands also include metabolites withincreased levels resulting from mutations in key metabolic enzymes inkidney cancer such as lactate, glutathione, kynurenine as disclosed byMinton, D R and Nanus, D M (Nature Reviews, Urology, Vol. 12, 2005,incorporated herein by reference). Aptamers have binding regions thatare capable of forming complexes with an intended target molecule (i.e.,the ligand). The specificity of the binding can be defined in terms ofthe comparative dissociation constants (Kd) of the aptamer for itsligand as compared to the dissociation constant of the aptamer forunrelated molecules. Thus, the ligand is a molecule that binds to theaptamer with greater affinity than to unrelated material. Typically, theKd for the aptamer with respect to its ligand will be at least about10-fold less than the Kd for the aptamer with unrelated molecules. Inother embodiments, the Kd will be at least about 20-fold less, at leastabout 50-fold less, at least about 100-fold less, and at least about200-fold less. An aptamer will typically be between about 15 and about200 nucleotides in length. More commonly, an aptamer will be betweenabout 30 and about 100 nucleotides in length.

The aptamers that can be incorporated as part of the riboswitch can be anaturally occurring aptamer, or modifications thereof, or aptamers thatare designed de novo and/or screened through systemic evolution ofligands by exponential enrichment (SELEX) or other screening methods.Examples of aptamers that bind small molecule ligands include, but arenot limited to theophylline, dopamine, sulforhodamine B, cellobiose,kanamycin A, lividomycin, tobramycin, neomycin B, viomycin,chloramphenicol, streptomycin, cytokines, cell surface molecules, andmetabolites. For a review of aptamers that recognize small molecules,see, e.g., Famulok, Science 9:324-9 (1999) and McKeague, M. & DeRosa, M.C. J. Nuc. Aci. 2012 (both of which are incorporated herein byreference). In another embodiment, the aptamer is a complementarypolynucleotide.

Methods for Identifying Aptamer/Ligand

In one embodiment, the aptamer is designed to bind a particular smallmolecule ligand. Methods for designing and selecting aptamers that bindparticular ligands are disclosed in 62/370,599, incorporated herein byreference. Other methods for screening aptamers include, for example,SELEX. Methods for designing aptamers that selectively bind a smallmolecule using SELEX are disclosed in, e.g., U.S. Pat. Nos. 5,475,096,5,270,163, and Abdullah Ozer, et al. Nuc. Aci. 2014, which areincorporated herein by reference. Modifications of the SELEX process aredescribed in U.S. Pat. Nos. 5,580,737 and 5,567,588, which areincorporated herein by reference.

Selection techniques for identifying aptamers generally involvepreparing a large pool of DNA or RNA molecules of the desired lengththat contain a region that is randomized or mutagenized. For example, anoligonucleotide pool for aptamer selection might contain a region of20-100 randomized nucleotides flanked by regions of defined sequencethat are about 15-25 nucleotides long and useful for the binding of PCRprimers. The oligonucleotide pool is amplified using standard PCRtechniques, or other means that allow amplification of selected nucleicacid sequences. The DNA pool may be transcribed in vitro to produce apool of RNA transcripts when an RNA aptamer is desired. The pool of RNAor DNA oligonucleotides is then subjected to a selection based on theirability to bind specifically to the desired ligand. Selection techniquesinclude, for example, affinity chromatography, although any protocolwhich will allow selection of nucleic acids based on their ability tobind specifically to another molecule may be used. Selection techniquesfor identifying aptamers that bind small molecules and function within acell may involve cell based screening methods. In the case of affinitychromatography, the oligonucleotides are contacted with the targetligand that has been immobilized on a substrate in a column or onmagnetic beads. The oligonucleotide is preferably selected for ligandbinding in the presence of salt concentrations, temperatures, and otherconditions which mimic normal physiological conditions. Oligonucleotidesin the pool that bind to the ligand are retained on the column or bead,and nonbinding sequences are washed away. The oligonucleotides that bindthe ligand are then amplified (after reverse transcription if RNAtranscripts were utilized) by PCR (usually after elution). The selectionprocess is repeated on the selected sequences for a total of about threeto ten iterative rounds of the selection procedure. The resultingoligonucleotides are then amplified, cloned, and sequenced usingstandard procedures to identify the sequences of the oligonucleotidesthat are capable of binding the target ligand. Once an aptamer sequencehas been identified, the aptamer may be further optimized by performingadditional rounds of selection starting from a pool of oligonucleotidescomprising a mutagenized aptamer sequence.

In vivo aptamer screening may be used following one or more rounds of invitro selection (e.g., SELEX). For example, Konig, J. et al. (RNA. 2007,13(4):614-622, incorporated herein by reference) describe combiningSELEX and a yeast three-hybrid system for in vivo selection of aptamer.

Target Genes

The gene regulation cassette of the present invention is a platform thatcan be used to regulate the expression of any target gene that can beexpressed in a target cell, tissue or organism. The term “target gene”refers to a polynucleotide that is introduced into a cell and is capableof being transcribed into RNA and translated and/or expressed underappropriate conditions. Alternatively, the target gene is endogenous tothe target cell and the gene regulation cassette of the presentinvention is positioned into the target gene (for example into the 5′ or3′ UTR of an endogenous target gene). An example of a target gene is apolynucleotide encoding a therapeutic polypeptide. In anotherembodiment, the target gene encodes an RNA such as a miRNA, rRNA, smallor long noncoding RNAs, short hairpin RNA (shRNA) and any otherregulatory RNAs. In one embodiment, the target gene is exogenous to thecell in which the recombinant DNA construct is to be transcribed. Inanother embodiment, the target gene is endogenous to the cell in whichthe recombinant DNA construct is to be transcribed.

The target gene according to the present invention may be a geneencoding a protein, or a sequence encoding a non-protein coding RNA. Thetarget gene may be, for example, a gene encoding a structural protein,an enzyme, a cell signaling protein, a mitochondrial protein, a zincfinger protein, a hormone, a transport protein, a growth factor, acytokine, an intracellular protein, an extracellular protein, atransmembrane protein, a cytoplasmic protein, a nuclear protein, areceptor molecule, an RNA binding protein, a DNA binding protein, atranscription factor, translational machinery, a channel protein, amotor protein, a cell adhesion molecule, a mitochondrial protein, ametabolic enzyme, a kinase, a phosphatase, exchange factors, a chaperoneprotein, and modulators of any of these. In embodiments, the target geneencodes erythropoietin (Epo), human growth hormone (hGH), transcriptionactivator-like effector nucleases (TALEN), human insulin, CRISPRassociated protein 9 (cas9), or an immunoglobulin (or portion thereof),including, e.g., a therapeutic antibody.

Expression Constructs

The present invention contemplates the use of a recombinant vector forintroduction into target cells of a polynucleotide encoding a targetgene and containing the gene regulation cassette described herein. Inmany embodiments, the recombinant DNA construct of this inventionincludes additional DNA elements including DNA segments that provide forthe replication of the DNA in a host cell and expression of the targetgene in that cell at appropriate levels. The ordinarily skilled artisanappreciates that expression control sequences (promoters, enhancers, andthe like) are selected based on their ability to promote expression ofthe target gene in the target cell. “Vector” means a recombinantplasmid, yeast artificial chromosome (YAC), mini chromosome, DNAmini-circle or virus (including virus derived sequences) that comprisesa polynucleotide to be delivered into a host cell, either in vitro or invivo. In one embodiment, the recombinant vector is a viral vector or acombination of multiple viral vectors.

Viral vectors for the aptamer-mediated expression of a target gene in atarget cell, tissue, or organism are known in the art and includeadenoviral (AV) vectors, adeno-associated virus (AAV) vectors,retroviral and lentiviral vectors, and Herpes simplex type 1 (HSV1)vectors.

Adenoviral vectors include, for example, those based on human adenovirustype 2 and human adenovirus type 5 that have been made replicationdefective through deletions in the E1 and E3 regions. Thetranscriptional cassette can be inserted into the E1 region, yielding arecombinant E1/E3-deleted AV vector. Adenoviral vectors also includehelper-dependent high-capacity adenoviral vectors (also known ashigh-capacity, “gutless” or “gutted” vectors), which do not containviral coding sequences. These vectors, contain the cis-acting elementsneeded for viral DNA replication and packaging, mainly the invertedterminal repeat sequences (ITR) and the packaging signal (Ψ). Thesehelper-dependent AV vector genomes have the potential to carry from afew hundred base pairs up to approximately 36 kb of foreign DNA.

Recombinant adeno-associated virus “rAAV” vectors include any vectorderived from any adeno-associated virus serotype, including, withoutlimitation, AAV-1, AAV-2, AAV-3, AAV-4, AAV-5, AAV-7 and AAV-8, AAV-9,AAV-10, and the like. rAAV vectors can have one or more of the AAVwild-type genes deleted in whole or in part, preferably the Rep and/orCap genes, but retain functional flanking ITR sequences. Functional ITRsequences are retained for the rescue, replication, packaging andpotential chromosomal integration of the AAV genome. The ITRs need notbe the wild-type nucleotide sequences, and may be altered (e.g., by theinsertion, deletion or substitution of nucleotides) so long as thesequences provide for functional rescue, replication and packaging.

Alternatively, other systems such as lentiviral vectors can be used inembodiments of the invention. Lentiviral-based systems can transducenon-dividing as well as dividing cells making them useful forapplications targeting, for examples, the non-dividing cells of the CNS.Lentiviral vectors are derived from the human immunodeficiency virusand, like that virus, integrate into the host genome providing thepotential for long-term gene expression.

Polynucleotides, including plasmids, YACs, minichromosomes andminicircles, carrying the target gene containing the gene regulationcassette can also be introduced into a cell or organism by nonviralvector systems using, for example, cationic lipids, polymers, or both ascarriers. Conjugated poly-L-lysine (PLL) polymer and polyethylenimine(PEI) polymer systems can also be used to deliver the vector to cells.Other methods for delivering the vector to cells includes hydrodynamicinjection and electroporation and use of ultrasound, both for cellculture and for organisms. For a review of viral and non-viral deliverysystems for gene delivery see Nayerossadat, N. et al. (Adv Biomed Res.2012; 1:27; incorporated herein by reference).

Methods of Modulating Expression of a Target Gene

In one aspect, this invention provides a method of modulating expressionof a target gene (e.g., a therapeutic gene), by (a) inserting the generegulation cassette of the present invention into the 3′ UTR of a targetgene; (b) introducing the target gene comprising the gene regulationcassette into a cell; and (c) exposing the cell to a ligand that bindsthe aptamer. In one embodiment, the ligand is a small molecule. Inaspects, expression of the target gene in target cells confers a desiredproperty to a cell into which it was introduced, or otherwise leads to adesired therapeutic outcome.

In one embodiment, one or more gene regulation cassettes are insertedinto the 3′ untranslated region of the target gene. In one embodiment, asingle gene regulation cassette is inserted into the 3′ UTR of a targetgene. In other embodiments 2, 3, 4, or more gene regulation cassettesare inserted in the target gene. In one embodiment, two gene regulationcassettes are inserted into the target gene. When multiple generegulation cassettes are inserted into a target gene, they each cancontain the same aptamer such that a single ligand can be used tomodulate ribonuclease cleavage of the multiple cassettes and therebymodulate target gene expression. In other embodiments, multiple generegulation cassettes are inserted into a target gene, each can contain adifferent aptamer so that exposure to multiple different small moleculeligands modulates target gene expression. In other embodiments, multiplegene regulation cassettes are inserted into a target gene, eachcontaining different ribonuclease substrate sequences. This may beuseful in reducing recombination and improving ease of incorporationinto viral vectors.

The polynucleotide cassettes of the present invention are effective atmodulating target gene expression when the polynucleotide cassette islocated in the 3′ UTR of the target gene at any location upstream (5′)of the polyadenylation signal (e.g., AATAAA). The polynucleotidecassette is also effective at modulating target gene expression byblocking polyadenylation when different poly(A) signal sequences arepresent, for example the SV40 early versus late poly(A) signals (see,e.g., Examples 4-6, 8). In one embodiment, the at least onepolynucleotide cassette of the present invention is inserted about 87 orabout 140 nucleotides 5′ of the polyadenylation sequence. In oneembodiment, a polynucleotide cassette of the present invention isinserted at, or near, both locations. In other embodiments, apolynucleotide cassette is inserted at one or more of about 74, about110, or about 149 nucleotides 5′ of the polyadenylation signal.

The polynucleotide cassette of the present invention can be used incombination with other mechanisms for the regulation of expression ofthe target gene. In one embodiment, a polynucleotide cassette of thepresent invention is used in combination with a gene regulation cassettethat modulates target gene expression by aptamer-mediated regulation ofalternative splicing as described in WO 2016/126747, incorporated hereinby reference.

Methods of Treatment and Pharmaceutical Compositions

One aspect of the invention provides a method of regulating the level ofa therapeutic protein delivered by gene therapy. In this embodiment, the“target gene” may encode the therapeutic protein. The “target gene” mayencode a protein that is endogenous or exogenous to the cell.

The therapeutic gene sequence containing the regulatory cassette withaptamer-driven riboswitch is delivered to target cells in vitro or exvivo, e.g., by a vector. The cell specificity of the “target gene” maybe controlled by promoter or other elements within the vector. Deliveryof the vector construct containing the target gene and thepolynucleotide cassette, and the transfection of the target tissuesresulting in stable transfection of the regulated target gene, is oftenthe first step in producing the therapeutic protein.

However, due to the presence of the regulatory cassette within thetarget gene sequence, the target gene is not expressed at significantlevels, i.e., it is in the “off state” in the absence of the specificligand that binds to the aptamer contained within in the regulatorycassette riboswitch. Only when the aptamer specific ligand isadministered (or otherwise present in sufficient quantities) is thetarget gene expression activated.

The delivery of the vector construct containing the target gene and thedelivery of the activating ligand generally are separated in time. Thedelivery of the activating ligand will control when the target gene isexpressed, as well as the level of protein expression. The ligand may bedelivered by a number of routes including, but not limited to, oral,intramuscular (IM), intravenous (IV), intraocular, or topically.

The timing of delivery of the ligand will depend on the requirement foractivation of the target gene. For example, if the therapeutic proteinencoded by the target gene is required constantly, an oral smallmolecule ligand may be delivered daily, or multiple times a day, toensure continual activation of the target gene, and thus continualexpression of the therapeutic protein. If the target gene has a longacting effect, the inducing ligand may be dosed less frequently.

This invention allows the expression of the therapeutic transgene to becontrolled temporally, in a manner determined by the temporal dosing ofthe ligand specific to the aptamer within the riboswitch of theregulatory polynucleotide cassette. The increased expression of thetherapeutic transgene only on ligand administration, increases thesafety of a gene therapy treatment by allowing the target gene to be offin the absence of the ligand.

Different aptamers can be used to allow different ligands to activatetarget genes. In certain embodiments of the invention, each therapeuticgene containing a regulatory cassette will have a specific aptamerwithin the cassette that will be activated by a specific small molecule.This means that each therapeutic gene can be activated only by theligand specific to the aptamer housed within it. In these embodiments,each ligand will only activate one therapeutic gene. This allows for thepossibility that several different “target genes” may be delivered toone individual and each will be activated on delivery of the specificligand for the aptamer contained within the regulatory cassette housedin each target gene.

This invention allows any therapeutic protein whose gene can bedelivered to the body (such as erythropoietin (EPO) or a therapeuticantibody) to be produced by the body when the activating ligand isdelivered. This method of therapeutic protein delivery may replace themanufacture of such therapeutic proteins outside of the body which arethen injected or infused, e.g., antibodies used in cancer or to blockinflammatory or autoimmune disease. The body containing the regulatedtarget gene becomes the biologics manufacturing factory, which isswitched on when the gene-specific ligand is administered.

Dosing levels and timing of dosing of a therapeutic protein may beimportant to therapeutic effect. For example, in the delivery of AVASTIN(anti-VEGF antibody) for cancer. The present invention increases theease of dosing in response to monitoring for therapeutic protein levelsand effects.

In one embodiment, the target gene may encode a nuclease that can targetand edit a particular DNA sequence. Such nucleases include Cas9, zincfinger containing nucleases, or TALENs. In the case of these nucleases,the nuclease protein may be required for only a short period of timethat is sufficient to edit the target endogenous genes. However, if anunregulated nuclease gene is delivered to the body, this protein may bepresent for the rest of the life of the cell. In the case of nucleases,there is an increasing risk of off-target editing the longer thenuclease is present. Regulation of expression of such proteins has asignificant safety advantage. In this case, vector containing thenuclease target gene containing a regulatory cassette could be deliveredto the appropriate cells in the body. The target gene is in the “off”state in the absence of the cassette-specific ligand, so no nuclease isproduced. Only when the activating ligand is administered, is thenuclease produced. When sufficient time has elapsed allowing sufficientediting to occur, the ligand will be withdrawn and not administeredagain. Thus, the nuclease gene is thereafter in the “off” state and nofurther nuclease is produced and editing stops. This approach may beused to correct genetic conditions, including a number of inheritedretinopathies such as LCA10 caused by mutations in CEP290 andStargardt's Disease caused by mutations in ABCA4.

Administration of a regulated target gene encoding a therapeutic proteinwhich is activated only on specific ligand administration may be used toregulate therapeutic genes to treat many different types of diseases,e.g., cancer with therapeutic antibodies, immune disorders with immunemodulatory proteins or antibodies, metabolic diseases, rare diseasessuch as PNH with anti-C5 antibodies or antibody fragments as theregulated gene, or ocular angiogenesis with therapeutic antibodies, anddry AMD with immune modulatory proteins.

A wide variety of specific target genes, allowing for the treatment of awide variety of specific diseases and conditions, are suitable for usein the present invention. For example, insulin or an insulin analog(preferably human insulin or an analog of human insulin) may be used asthe target gene to treat type I diabetes, type II diabetes, or metabolicsyndrome; human growth hormone may be used as the target gene to treatchildren with growth disorders or growth hormone-deficient adults;erythropoietin (preferably human erythropoietin) may be used as thetarget gene to treat anemia due to chronic kidney disease, anemia due tomyelodysplasia, or anemia due to cancer chemotherapy.

The present invention may be especially suitable for treating diseasescaused by single gene defects such as cystic fibrosis, hemophilia,muscular dystrophy, thalassemia, or sickle cell anemia. Thus, human (β-,γ-, δ-, or ζ-globin may be used as the target gene to treatβ-thalassemia or sickle cell anemia; human Factor VIII or Factor IX maybe used as the target gene to treat hemophilia A or hemophilia B.

The ligands used in the present invention are generally combined withone or more pharmaceutically acceptable carriers to form pharmaceuticalcompositions suitable for administration to a patient. Pharmaceuticallyacceptable carriers include solvents, binders, diluents, disintegrants,lubricants, dispersion media, coatings, antibacterial and antifungalagents, isotonic and absorption delaying agents, and the like, generallyused in the pharmaceutical arts. Pharmaceutical compositions may be inthe form of tablets, pills, capsules, troches, and the like, and areformulated to be compatible with their intended route of administration.Examples of routes of administration include parenteral, e.g.,intravenous, intradermal, intranasal, subcutaneous, oral, inhalation,transdermal (topical), transmucosal, and rectal.

The pharmaceutical compositions comprising ligands are administered to apatient in a dosing schedule such that an amount of ligand sufficient todesirably regulate the target gene is delivered to the patient. When theligand is a small molecule and the dosage form is a tablet, capsule, orthe like, preferably the pharmaceutical composition comprises from 0.1mg to 10 g of ligand; from 0.5 mg to 5 g of ligand; from 1 mg to 1 g ofligand; from 2 mg to 750 mg of ligand; from 5 mg to 500 mg of ligand; orfrom 10 mg to 250 mg of ligand.

The pharmaceutical compositions may be dosed once per day or multipletimes per day (e.g., 2, 3, 4, 5, or more times per day). Alternatively,pharmaceutical compositions may be dosed less often than once per day,e.g., once every 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, or 14 days, oronce a month or once every few months. In some embodiments of theinvention, the pharmaceutical compositions may be administered to apatient only a small number of times, e.g., once, twice, three times,etc.

The present invention provides a method of treating a patient in need ofincreased expression of a therapeutic protein encoded by a target gene,the method comprising administering to the patient a pharmaceuticalcomposition comprising a ligand for an aptamer, where the patientpreviously had been administered a recombinant DNA comprising the targetgene, where the target gene contains a gene regulation cassette of thepresent invention that provides the ability to regulate expression ofthe target gene by the ligand of the aptamer by alternative splicing ofpre-mRNA of the target gene, thereby increasing expression of thetherapeutic protein.

Articles of Manufacture and Kits

Also provided are kits or articles of manufacture for use in the methodsdescribed herein. In aspects, the kits comprise the compositionsdescribed herein (e.g., for compositions for delivery of a vectorcomprising the target gene containing the gene regulation cassette) insuitable packaging. Suitable packaging for compositions (such as ocularcompositions for injection) described herein are known in the art, andinclude, for example, vials (such as sealed vials), vessels, ampules,bottles, jars, flexible packaging (e.g., sealed Mylar or plastic bags),and the like. These articles of manufacture may further be sterilizedand/or sealed.

The present invention also provides kits comprising compositionsdescribed herein and may further comprise instruction(s) on methods ofusing the composition, such as uses described herein. The kits describedherein may further include other materials desirable from a commercialand user standpoint, including other buffers, diluents, filters,needles, syringes, and package inserts with instructions for performingthe administration, including e.g., any methods described herein. Forexample, in some embodiments, the kit comprises rAAV for expression ofthe target gene comprising the gene regulation cassette of the presentinvention, a pharmaceutically acceptable carrier suitable for injection,and one or more of: a buffer, a diluent, a filter, a needle, a syringe,and a package insert with instructions for performing the injections. Insome embodiments, the kit is suitable for intraocular injection,intramuscular injection, intravenous injection and the like.

“Homology” and “homologous” as used herein refer to the percent ofidentity between two polynucleotide sequences or between two polypeptidesequences. The correspondence between one sequence to another can bedetermined by techniques known in the art. For example, homology can bedetermined by a direct comparison of two polypeptide molecules byaligning the sequence information and using readily available computerprograms. Two polynucleotide or two polypeptide sequences are“substantially homologous” to each other when, after optimally alignedwith appropriate insertions or deletions, at least about 80%, at leastabout 85%, at least about 90%, and at least about 95% of the nucleotidesor amino acids, respectively, match over a defined length of themolecules, as determined using the methods above.

“Percent sequence identity” with respect to a reference polypeptide ornucleic acid sequence is defined as the percentage of amino acidresidues or nucleotides in a candidate sequence that are identical withthe amino acid residues or nucleotides in the reference polypeptide ornucleic acid sequence, after aligning the sequences and introducinggaps, if necessary, to achieve the maximum percent sequence identity.Alignment for purposes of determining percent amino acid or nucleic acidsequence identity can be achieved in ways known to theordinarily-skilled artisan, for example, using publicly availablecomputer software programs including BLAST, BLAST-2, ALIGN or Megalign(DNASTAR) software.

The term “polynucleotide” or “nucleic acid” as used herein refers to apolymeric form of nucleotides of any length, either ribonucleotides ordeoxyribonucleotides. Thus, this term includes, but is not limited to,single-, double- or multi-stranded DNA or RNA, genomic DNA, cDNA,DNA-RNA hybrids, or a polymer comprising purine and pyrimidine bases, orother natural, chemically or biochemically modified, non-natural, orderivatized nucleotide bases.

“Heterologous” or “exogenous” means derived from a genotypicallydistinct entity from that of the rest of the entity to which it iscompared or into which it is introduced or incorporated. For example, apolynucleotide introduced by genetic engineering techniques into adifferent cell type is a heterologous polynucleotide (and, whenexpressed, can encode a heterologous polypeptide). Similarly, a cellularsequence (e.g., a gene or portion thereof) that is incorporated into aviral vector is a heterologous nucleotide sequence with respect to thevector.

The below table contains a listing of the DNA sequences of theconstructs described herein as well as other sequences as described. TheU1 binding site and its mutant sequence are in grey highlighted lowercase letters; the stem-loop structure (SL) is in underlined lower caseletters; aptamer sequences are in wave underlined lower case letters;poly(A) signal sequence is in thick underlined lower case letters; andcoding sequences for luciferase genes are in upper case letters.

SEQ ID NO.: Description Sequence 1 Consensus U1 CAGGTAAGTA binding site2 Mutant U1 binding CATGGAACTA site 3 U1-87 wt in pRL-TCAAATCGTTCGTTGAGCGAGTTCTCAAAAATGAA SV40CAATAAttctagagcggccgcttcgagcagacatgataagatacattgatgagt

atttgtgatgctattgctttatttgtaaccattataagctgcaataaacaagttaacaacaa c 4U1-87 mut in pRL- TCAAATCGTTCGTTGAGCGAGTTCTCAAAAATGAA SV40CAATAAttctagagcggccgcttcgagcagacatgataagatacattgatgagt

tttgtgatgctattgctttatttgtaaccattataagctgcaataaacaagttaacaacaac 5U1-140 wt in pRL- TCAAATCGTTCGTTGAGCGAGTTCTCAAAAATGAA SV40

cattgatgagtttggacaaaccacaactagaatgcagtgaaaaaaatgctttatttgtgaaatttgtgatgctattgctttatttgtaaccattataagctgcaataaacaagttaacaac aac 6U1-140 mut in TCAAATCGTTCGTTGAGCGAGTTCTCAAAAATGAA pRL-SV40

cattgatgagtttggacaaaccacaactagaatgcagtgaaaaaaatgctttatttgtg

aac 7 2xU1-140 wt in TCAAATCGTTCGTTGAGCGAGTTCTCAAAAATGAA pRL-SV40

cagacatgataagatacattgatgagtttggacaaaccacaactagaatgcagtgaa

8 2xU1-140 mut in TCAAATCGTTCGTTGAGCGAGTTCTCAAAAATGAA pRL-SV40

cagacatgataagatacattgatgagtttggacaaaccacaactagaatgcagtgaa

9 3xU1-140 wt in TCAAATCGTTCGTTGAGCGAGTTCTCAAAAATGAA pRL-SV40

actagaatgcagtgaaaaaaatgctttatttgtgaaatttgtgatgctattgctttatttgtaaccattataagctgcAATAAAcaagttaacaacaac 10 3xU1_140 mut inTCAAATCGTTCGTTGAGCGAGTTCTCAAAAATGAA pRL-SV40

actagaatgcagtgaaaaaaatgctttatttgtgaaatttgtgatgctattgctttatttgtaaccattataagctgcAATAAAcaagttaacaacaac 11 87-9 in pRL-SV40TCAAATCGTTCGTTGAGCGAGTTCTCAAAAATGAACAATAAttctagagcggccgcttcgagcagacatgataagatacattgatgagt

12 87-8 in pRL-SV40 TCAAATCGTTCGTTGAGCGAGTTCTCAAAAATGAACAATAAttctagagcggccgcttcgagcagacatgataagatacattgatgagt

13 87-7 in pRL-SV40 TCAAATCGTTCGTTGAGCGAGTTCTCAAAAATGAACAATAAttctagagcggccgcttcgagcagacatgataagatacattgatgagt

14 87-6 in pRL-SV40 TCAAATCGTTCGTTGAGCGAGTTCTCAAAAATGAACAATAAttctagagcggccgcttcgagcagacatgataagatacattgatgagt

15 87-5 in pRL-SV40 TCAAATCGTTCGTTGAGCGAGTTCTCAAAAATGAACAATAAttctagagcggccgcttcgagcagacatgataagatacattgatgagt

16 U1 87-9 SL in TCAAATCGTTCGTTGAGCGAGTTCTCAAAAATGAA pRL-SV40CAATAAttctagagcggccgcttcgagcagacatgataagatacattgatgagtttggacaaaccaaacccaggtaagttaccgaaaggtaacttacctgggcaactagaatgcagtgaaaaaaatgctttatttgtgaaatttgtgatgctattgctttatttgtaaccatta

17 U1 87-9 SL broken TCAAATCGTTCGTTGAGCGAGTTCTCAAAAATGAA in pRL-SV40CAATAAttctagagcggccgcttcgagcagacatgataagatacattgatgagtttggacaaaccaaacccaggtaagttaccgaaaaaaacaaacaaaaaacaactagaatgcagtgaaaaaaatgctttatttgtgaaatttgtgatgctattgctttatttgtaaccatt

18 U1_theo_1 in pRL- TCAAATCGTTCGTTGAGCGAGTTCTCAAAAATGAA SV40CAATAAttctagagcggccgcttcgagcagacatgataagatacattgatgagt

c 19 U1_theo_2 in pRL- TCAAATCGTTCGTTGAGCGAGTTCTCAAAAATGAA SV40CAATAAttctagagcggccgcttcgagcagacatgataagatacattgatgagt

20 U1_theo_3 in pRL- TCAAATCGTTCGTTGAGCGAGTTCTCAAAAATGAA SV40CAATAAttctagagcggccgcttcgagcagacatgataagatacattgatgagt

21 U1_theo_4 in pRL- TCAAATCGTTCGTTGAGCGAGTTCTCAAAAATGAA SV40CAATAAttctagagcggccgcttcgagcagacatgataagatacattgatgagt

22 U1_theo_5 in pRL- TCAAATCGTTCGTTGAGCGAGTTCTCAAAAATGAA SV40CAATAAttctagagcggccgcttcgagcagacatgataagatacattgatgagt

taacttacctgggcaactagaatgcagtgaaaaaaatgctttatttgtgaaatttgtgat

23 U1_theo_6 in pRL- TCAAATCGTTCGTTGAGCGAGTTCTCAAAAATGAA SV40CAATAAttctagagcggccgcttcgagcagacatgataagatacattgatgagt

acttacctgggcaactagaatgcagtgaaaaaaatgctttatttgtgaaatttgtgatgc

24 U1_theo_7 in pRL- TCAAATCGTTCGTTGAGCGAGTTCTCAAAAATGAA SV40CAATAAttctagagcggccgcttcgagcagacatgataagatacattgatgagt

ttacctgggcaactagaatgcagtgaaaaaaatgctttatttgtgaaatttgtgatgctat

25 U1_theo_8 in pRL- TCAAATCGTTCGTTGAGCGAGTTCTCAAAAATGAA SV40CAATAAttctagagcggccgcttcgagcagacatgataagatacattgatgagt

acctgggcaactagaatgcagtgaaaaaaatgctttatttgtgaaatttgtgatgctatt

26 U1_theo_9 in pRL- TCAAATCGTTCGTTGAGCGAGTTCTCAAAAATGAA SV40CAATAAttctagagcggccgcttcgagcagacatgataagatacattgatgagt

ctgggcaactagaatgcagtgaaaaaaatgctttatttgtgaaatttgtgatgctattgc

27 U1_theo_8_1 in TCAAATCGTTCGTTGAGCGAGTTCTCAAAAATGAA pRL-SV40CAATAAttctagagcggccgcttcgagcagacatgataagatacattgatgagt

acctggacaactagaatgcagtgaaaaaaatgctttatttgtgaaatttgtgatgctatt

28 U1_theo_8_2 in TCAAATCGTTCGTTGAGCGAGTTCTCAAAAATGAA pRL-SV40CAATAAttctagagcggccgcttcgagcagacatgataagatacattgatgagt

acctgaacaactagaatgcagtgaaaaaaatgctttatttgtgaaatttgtgatgctatt

29 U1_theo_8_3 in TCAAATCGTTCGTTGAGCGAGTTCTCAAAAATGAA pRL-SV40CAATAAttctagagcggccgcttcgagcagacatgataagatacattgatgagt

acctaaacaactagaatgcagtgaaaaaaatgctttatttgtgaaatttgtgatgctatt

30 U1_theo_8_4 in TCAAATCGTTCGTTGAGCGAGTTCTCAAAAATGAA pRL-SV40CAATAAttctagagcggccgcttcgagcagacatgataagatacattgatgagt

accaaaacaactagaatgcagtgaaaaaaatgctttatttgtgaaatttgtgatgctatt

31 U1_theo_8_5 in TCAAATCGTTCGTTGAGCGAGTTCTCAAAAATGAA pRL-SV40CAATAAttctagagcggccgcttcgagcagacatgataagatacattgatgagt

acaaaaacaactagaatgcagtgaaaaaaatgctttatttgtgaaatttgtgatgctatt

32 U1_theo_8_6 in TCAAATCGTTCGTTGAGCGAGTTCTCAAAAATGAA pRL-SV40CAATAAttctagagcggccgcttcgagcagacatgataagatacattgatgagt

aaaaaaacaactagaatgcagtgaaaaaaatgctttatttgtgaaatttgtgatgctatt

33 U1_theo_8_7 in TCAAATCGTTCGTTGAGCGAGTTCTCAAAAATGAA pRL-SV40CAATAAttctagagcggccgcttcgagcagacatgataagatacattgatgagt

caaaaaacaactagaatgcagtgaaaaaaatgattatttgtgaaatttgtgatgctatt

34 U1_theo_8_8 in TCAAATCGTTCGTTGAGCGAGTTCTCAAAAATGAA pRL-SV40CAATAAttctagagcggccgcttcgagcagacatgataagatacattgatgagt

caaaaaacaactagaatgcagtgaaaaaaatgattatttgtgaaatttgtgatgctatt

35 U1_theo_8_9 in TCAAATCGTTCGTTGAGCGAGTTCTCAAAAATGAA pRL-SV40CAATAAttctagagcggccgcttcgagcagacatgataagatacattgatgagt

acaaaaaacaactagaatgcagtgaaaaaaatgattatttgtgaaatttgtgatgctat

36 U1_theo_9_1 in TCAAATCGTTCGTTGAGCGAGTTCTCAAAAATGAA pRL-SV40CAATAAttctagagcggccgcttcgagcagacatgataagatacattgatgagt

ctggacaactagaatgcagtgaaaaaaatgctttatttgtgaaatttgtgatgctattgct

37 U1_theo_9_2 in TCAAATCGTTCGTTGAGCGAGTTCTCAAAAATGAA pRL-SV40CAATAAttctagagcggccgcttcgagcagacatgataagatacattgatgagt

ctgaacaactagaatgcagtgaaaaaaatgattatttgtgaaatttgtgatgctattgct

38 U1_theo_9_3 in TCAAATCGTTCGTTGAGCGAGTTCTCAAAAATGAA pRL-SV40CAATAAttctagagcggccgcttcgagcagacatgataagatacattgatgagt

ctaaacaactagaatgcagtgaaaaaaatgattatttgtgaaatttgtgatgctattgct

39 U1_theo_9_4 in TCAAATCGTTCGTTGAGCGAGTTCTCAAAAATGAA pRL-SV40CAATAAttctagagcggccgcttcgagcagacatgataagatacattgatgagt

caaaacaactagaatgcagtgaaaaaaatgattatttgtgaaatttgtgatgctattgc

40 U1_theo_9_5 in TCAAATCGTTCGTTGAGCGAGTTCTCAAAAATGAA pRL-SV40CAATAAttctagagcggccgcttcgagcagacatgataagatacattgatgagt

aaaaacaactagaatgcagtgaaaaaaatgattatttgtgaaatttgtgatgctattgc

41 U1_theo_9_6 in TCAAATCGTTCGTTGAGCGAGTTCTCAAAAATGAA pRL-SV40CAATAAttctagagcggccgcttcgagcagacatgataagatacattgatgagt

aaaaacaactagaatgcagtgaaaaaaatgattatttgtgaaatttgtgatgctattgc

42 U1_theo_9_7 in TCAAATCGTTCGTTGAGCGAGTTCTCAAAAATGAA pRL-SV40CAATAAttctagagcggccgcttcgagcagacatgataagatacattgatgagt

aaaaacaactagaatgcagtgaaaaaaatgctttatttgtgaaatttgtgatgctattgc

43 U1_theo_9_8 in TCAAATCGTTCGTTGAGCGAGTTCTCAAAAATGAA pRL-SV40CAATAAttctagagcggccgcttcgagcagacatgataagatacattgatgagt

aaaaacaactagaatgcagtgaaaaaaatgctttatttgtgaaatttgtgatgctattgc

44 4xU1_theo_8_1 in TCAAATCGTTCGTTGAGCGAGTTCTCAAAAATGAA pRL-SV40CAATAAttctagagcggccgcttcgagcagacatgataagatacattgatgagt

acctggacaactagaatgcagtgaaaaaagagtttggacaaaccaaacccaggtaa

45 U1_Gua_1 wt in TCATAAAGGCCAAGAAGGGCGGAAAGATCGCCGT pFLuc

cctcccacacctccccctgaacctgaaacataaaatgaatgcaattgttgttgttaactt

46 U1_Gua_1 mut in TCATAAAGGCCAAGAAGGGCGGAAAGATCGCCGT pFLuc

cctcccacacctccccctgaacctgaaacataaaatgaatgcaattgttgttgttaactt

47 U1_Gua_2 wt in TCATAAAGGCCAAGAAGGGCGGAAAGATCGCCGT pFLucGTAAgccataccacatttgtagaggttttacttgctttaaaaaacctcccacaccta

48 U1_Gua_2 mut in TCATAAAGGCCAAGAAGGGCGGAAAGATCGCCGT pFLucGTAAgccataccacatttgtagaggttttacttgctttaaaaaacctcccacaccta

49 U1_Gua_3 wt in TCATAAAGGCCAAGAAGGGCGGAAAGATCGCCGT pFLucGTAAgccataccacatttgtagaggttttacttgctttaaaaaacctcccacacctc

50 U1_Gua_3 mut in TCATAAAGGCCAAGAAGGGCGGAAAGATCGCCGT pFLucGTAAgccataccacatttgtagaggttttacttgctttaaaaaacctcccacacctc

51 wtU1_Gua_HBGP TCATAAAGGCCAAGAAGGGCGGAAAGATCGCCGT A

gatctaattcaccccaccagtgcaggctgcctatcagaaagtggtggctggtgtggctaatgccctggcccacaagtatcactaagctcgctttcttgctgtccaatttctattaaaggttcctttgttccctaagtccaactactaaactgggggatattatgaagggccttgagc

52 mutU1_Gua_HBG TCATAAAGGCCAAGAAGGGCGGAAAGATCGCCGT PA

gatctaattcaccccaccagtgcaggctgcctatcagaaagtggtggctggtgtggctaatgccctggcccacaagtatcactaagctcgctttcttgctgtccaatttctattaaaggttcctttgttccctaagtccaactactaaactgggggatattatgaagggccttgagc

It is to be understood and expected that variations in the principles ofinvention herein disclosed can be made by one skilled in the art and itis intended that such modifications are to be included within the scopeof the present invention. The following Examples further illustrate theinvention, but should not be construed to limit the scope of theinvention in any way. All references cited herein are herebyincorporated by reference in their entirety.

EXAMPLE 1

Effects on target gene expression of location and copy number of U1binding site in 3′ UTR

Experimental procedure:

Plasmid constructs: oligonucleotides (oligos) containing either wildtype consensus U1 binding sequence or its mutant sequence weresynthesized (IDT). The synthesized oligos were cloned into the 3′ UTR ofthe pRL-SV40 luciferase expression vector (Promega) using GibsonAssembly Cloning Kit (NEB). Constructs were purified (Qiagen) andverified by DNA sequencing (Genewiz).

Transfection: 3.5×10⁴ HEK 293 cells were plated in a 96-well flat bottomplate the day before transfection. Plasmid DNA (500 ng) was added to atube or a 96-well U-bottom plate. Separately, TransIT-293 reagent(Mirus; 1.4 μl) was added to 50 μl Opti-mem I media (Life Technologies),and allowed to sit for 5 minutes at room temperature (“RT”). Then, 50 μlof this diluted transfection reagent was added to the DNA, mixed, andincubated at RT for 20 min. Finally, 7 μl of this solution was added toa well of cells in the 96-well plate.

Renilla luciferase assay of cultured cells: 24 hours after the mediachange, plates were removed from the incubator, and equilibrated to RTfor several minutes on a lab bench, and the media aspirated. Glo-lysisbuffer (Promega, 100 μl, RT) was added, and the plates allowed to remainat room temp for at least 5 minutes. Then, the well contents were mixedby 50 μl trituration, and 20 μl of each well was mixed with 20 μl ofRenilla-glo reagent in a solid-white 384-well plate. Ten minutes later,luminescence was measured using a Tecan machine with 500 msec read time.The luciferase activity was expressed as mean relative light unit(RLU)±SD.

Results:

In order to build a U1-polyadenylation-based gene regulation platform, aU1 binding sequence was inserted into the 3′ UTR of a target reportergene. The 10 nucleotide (“nt”) consensus U1 binding sequence (referredto herein as wildtype or wt) was placed either 87 nt (U1-87) or 140 nt(U1-140) upstream of the AATAAA poly(A) sequence in the 3′ UTR in of theluciferase gene in the pRL-SV40 vector, as shown in FIG. 1 a. As shownin FIG. 1 b, insertion of 10-nt mutant U1 binding sequence at -87position (U1-87 mut) did not have any suppressive effect on luciferasegene expression compared to expression from the unmodified pRL-SV40construct. However, insertion of a 10-nt wild type U1 binding sequenceat the -87 position (U1-87 wt) inhibited 98% of Renilla luciferaseexpression when compared to luciferase activity from the pRL-SV40control vector. When compared with the U1-87 mut construct, the U1-87 wtgenerated 50-fold decrease in luciferase activity. Similarly, the mutantU1 site at -140 (U1-140 mut) did not cause inhibition of luciferase geneexpression. However, the wild type U1 binding sequence at the -140location (U1-140 wt) resulted in 91% inhibition of luciferase activity,generating 12-fold inhibition of luciferase activity when compared tothe U1-140 mut.

The inhibitory effect of either 2 copies or 3 copies of U1 bindingsequence inserted at -140 in 3′ UTR was also tested. As shown in FIG. 1b, 2 copies (2×U1-140 wt) or 3 copies (3×U1-140 wt) of the wild type U1binding sequence resulted in further reduction in luciferase activitywhen compared to single copy of U1 site at the same location (U1-140wt), generating 272-fold and 462-fold inhibition, respectively, whencompared to their corresponding mutant constructs. Thus, these resultsindicate that multiple copies of U1 binding sequence have synergisticfunction in suppressing gene expression.

EXAMPLE 2

Effect on target gene expression of the length of U1 binding sequence inthe 3′ UTR.

Experimental procedures: as described in Example 1.

Results:

Based on the results described in Example 1, the suppressive effect of aU1 binding site inserted 87 nt (U1-87) upstream of the SV40 late polyAsignal sequence was further characterized. In order to determine theminimal length of the U1 binding sequence for repressing target geneexpression when placed in the 3′, a series of constructs containing 3′sequentially-truncated sequence of U1 site, as shown in FIG. 2a . Asshown in FIG. 2 b, 9-nt U1 site (87-9) functioned as well as the 10-ntU1 site (U1-87). However, when the U1 binding sequence was truncated to8 nt, the suppressive effect of the U1 site was somewhat reduced,resulting in 3-fold less efficiency. When the U1 site sequence was 7 ntor shorter, the suppressive effect was significantly less efficient.These results indicate that U1 binding site inserted 87 nt upstream ofSV40 late poly(A) signal in 3′ UTR is more effective at repressingtarget gene expression when at least 8 nt long in order to recruit U1snRNP efficiently to suppress polyadenylation. A 9 nt U1 bindingsequence inserted 87 nt upstream of SV40 late polyA signal sequence wasselected for further characterization.

EXAMPLE 3

The effect of stem-loop secondary structure formation at the U1 site in3′ UTR on gene expression

Experimental Procedure:

The stem-loop sequences containing a wild type 9 nt U1 binding sequencewere synthesized (IDT) and cloned into pRL-SV40 vector. The constructsequences were verified by DNA sequencing (Genewiz). HEK 293 cells weretransfected and Renilla luciferase assay were performed as described inExample 1.

Results:

To determine the effect of a hairpin or stem-loop structure on the U1site-mediated suppression of gene expression, the 9 nt U1 site wasembedded in a stem-loop (SL) structure. In this stem-loop structure, asshown in FIG. 3a , the U1 site and its complementary sequence forms thestem. A mutant sequence was made as control in which no stem is formed(SL broken). As shown in FIG. 3b , embedding the 9 nt U1 site in thestem-loop structure (U1 87-9 SL) completely abolished the suppressiveeffect of the U1 site in the 3′ UTR, whereas the control sequence thatcan't form stem-loop structure (U1 87-9 SL broken) showed little effecton the suppressive function of U1 site. These results support that a U1site embedded in stem-loop structure is not accessible to U1 snRNPbinding, therefore gene expression is not suppressed by U1snRNP-mediated suppression of polyadenylation.

EXAMPLE 4

Use of theophylline aptamer to regulate target gene expression viamodulating U1 interference with polyadenylation

Experimental procedures:

Oligonucleotides containing either the full length of sequences of thestem from the stem-loop structure and theophylline aptamer or thetruncated sequences of the stem, were synthesized (IDT) and cloned intopRL-SV40 vector using the Gibson Assembly Cloning Kit (NEB). Constructsequences were verified by DNA sequencing (Genewiz). Transfection andaptamer ligand treatment: HEK 293 cells were transfected as described inExample 1. Four hours after transfection, the media was aspirated, andnew media with or without 3 mM theophylline was added. A Renillaluciferase assay was performed 20 to 24 hours after theophyllinetreatment as described in Example 1. The induction fold was expressed asthe quotient of luciferase activity obtained in the presence of aptamerligand divided by the value obtained in the absence of the aptamerligand.

Results:

In order to regulate the accessibility of a U1 site in the 3′ UTR of atarget gene, and thereby regulate target gene expression, the stemsequence of the aptamer structure was linked directly to the stem of thestem-loop structure tested in Example 3. In this configuration, asillustrated in FIG. 4a , insertion of aptamer sequence disrupts theformation of the stem structure, therefore, the U1 site in the 3′ UTR isaccessible to U1 snRNP binding. However, in the presence of aptamerligand, aptamer/ligand binding causes a RNA structure conformationalchange, facilitating stem formation and sequestering U1 site from U1snRNP binding in 3′ UTR.

A synthetic theophylline aptamer was tested in this configuration bylinking the lower stem sequence of the theophylline aptamer structure tothe stem of the stem-loop structure, which generated a 19 base pair stemas shown in FIG. 4b . We rationalized that if the stem is too long, thestem formation could be independent of the existence of aptamer sequenceand occur in the absence of aptamer ligand. Conversely, if the stem istoo short, even in the presence of aptamer ligand, a stable aptamerstructure cannot be achieved. Therefore, to determine an optimal lengthof the stem (including any stem from the aptamer and the stem containingU1 binding site), serial truncations to the stem were made, generating 9constructs with the length of the stem ranging from 19 to 11 bp. Asshown in FIG. 4c , with constructs U1_theo_1 through U1_theo_6, theluciferase activity was not suppressed significantly comparing toconstruct U1 87-9 in the absence of theophylline, suggesting thesequestering of the U1 site due to stem formation. Further, there was noincrease in the luciferase activity after theophylline treatment.However, in construct 8 and 9, the luciferase activity was increasedafter theophylline treatment, suggesting aptamer/ligand binding furtherblocks U1 site accessibility, leading to increased target geneexpression.

EXAMPLE 5

Optimization of the stem sequence to enhance the regulatability of U1accessibility due to aptamer/ligand binding

Experimental procedures: As described in Example 4.

Results:

Constructs U1_theo_8 and 9 showed small increase in luciferase activityafter theophylline treatment. To further enhance the regulatability ofthe U1 site accessibility when the aptamer is not bound by ligand, thestem structure was weakened by sequentially mutating the stem bases, asshown in FIG. 5a . Though, this strategy did not improve the inductionof luciferase activity from construct U1_theo_9, as shown in FIG. 5c ,it improved regulatability of construct U1_theo_8. As shown in FIG. 5b ,in a series of 9 constructs made from U1_theo_8, constructs U1_theo_8_1through 5 generated increased luciferase activity after theophyllinetreatment when compared to luciferase activity in the absence of aptamerligand. The induction fold was increased when comparing with theinduction fold of U1_theo_8 construct (1.3 fold), ranging from 1.8 to2.6 fold. Therefore, we have built a synthetic riboswitch that regulatesU1 interference with polyadenylation through aptamer/ligand binding.

EXAMPLE 6

Effects of multiple U1_theo riboswitch on regulating target geneexpression

Experimental procedures:

Oligos containing 4 copies of the U1_theo_8_1 sequence in tandem weresynthesized (IDT) and cloned using Gibson strategy and cloning kit(NEB). HEK 293 cells were transfected and Renilla luciferase assay wasperformed as described in Example 4.

Results:

Construct U1_theo_8-1 generated 1.8-fold induction after theophyllinetreatment, due to relatively high basal level expression of luciferasegene. In order to lower the basal level expression of the target gene, 4copies of the U1_theo_8_1 sequence was placed in tandem in the 3′ UTR,as shown in FIG. 6a . Indeed, as shown in FIG. 6b , 4 copies ofU1-theo_8_1 did reduce the basal level expression by 83% comparing tothe single copy of U1_theo_8_1. Upon theophylline treatment, the 4-copyconstruct increased the luciferase activity in a dose-dependent manner,generating 40% of the luciferase activity of 87-9 SL control vector andmaximal 4.3-fold induction at 6 mM theophylline. These results indicatethat multiple copies of the U1 site riboswitch in tandem can reducebasal expression level of the target gene, improving target generegulatability. In the current construct configuration, the same aptamersequence was used in all 4 copies of regulation cassettes. Differentaptamer sequences can be used in each copy of the riboswitch.

EXAMPLE 7

Use of xpt-guanine aptamer to regulate target gene expression viamodulating U1 interference

Experimental procedures:

Plasmid constructs: The EGFP gene in pEGFP-C1 vector was replaced withfirefly luciferase gene coding sequence to generate a pFLuc vector thatcontains an SV40 early polyadenylation signal sequence. Oligoscontaining either wild type or mutant U1 binding site from the 5′ splicesite of human DHFR exon 2 and xpt-guanine aptamer sequence followed bythe complementary sequence of the last 7 nt of the U1 site sequence weresynthesized (IDT) and cloned into the pFLuc vector using the Gibsoncloning strategy and kit (NEB).

Transfection and aptamer ligand treatment: HEK 293 cells weretransfected as described in Example 1. Four hours after transfection,the media was aspirated, and new media with or without 500 μM guaninewas added.

Firefly luciferase assay of cultured cells: Twenty-four hours after themedia change, the plates were removed from the incubator, andequilibrated to RT for several minutes on a lab bench, then aspirated.Glo-lysis buffer (Promega, 100 uL, RT) was added, and the plates allowedto remain at RT for at least 5 minutes. Then, the well contents weremixed by 50 uL trituration, and 20 uL of each sample was mixed with 20μL of bright-glo reagent (Promega) that had been diluted to 10% inglo-lysis buffer. The 96 wells were spaced on an opaque white 384-wellplate. Following a 5 min incubation at RT, luminescence was measuredusing a Tecan machine with 500 mSec read time. The luciferase activitywas expressed as mean relative light unit (RLU)±S.D.

Results:

The use of additional aptamer/ligand pair, either synthetic or naturalaptamers, in this U1-interference based, gene regulation platform wastested by inserting a 10 nt U1 site, the 5′ splice site from DHFR exon2, linked with xpt-guanine aptamer at different positions in pRLucvector, as shown in FIG. 7a . In this 10 nt U1 site, only the last 7 ntwere designed to base pair with its complementary sequence located atthe 3′ end of xpt-guanine aptamer sequence, as shown in FIG. 7b . Thissequence configuration was generated through a serial truncation of thestem sequence connecting the aptamer P1 stem and stem formed by the U1site and its complementary sequence, and demonstrated high dynamic rangein alternative splicing based aptamer riboswitch. In this study, weplaced this sequence configuration at either 149 nt, 110 nt or 74 ntupstream of the SV40 early poly(A) signal sequence in 3′ UTR region,generating U1_Guan_1, 2 and 3 constructs. In addition, a mutant U1 sitewas generated as a control sequence. As shown in FIG. 7c , upon guaninetreatment, the luciferase activity increased 2.4, 2.0 and 1.7 fold fromU1_Gua_1, 2, and 3 constructs, respectively.

EXAMPLE 8

Aptamer-modulated U1 interference is not polyA sequence specific

Experimental procedures:

Plasmid constructs: SV40 early polyadenylation sequence was replacedwith human beta globin polyA sequence in pFLuc vector to generatepFLuc_HBGPA. Oligos containing either wild type or mutant U1 bindingsite from 5′ ss of human DHFR exon 2 and xpt-guanine aptamer sequencefollowed by the complementary sequence of last 7 nt of U1 site sequencewere synthesized (IDT) and cloned into pFLuc_HBGPA vector using Gibsoncloning strategy and kit (NEB).

Transfection and luciferase assay were as described in Example 7.

Results:

We have demonstrated aptamer-modulated U1 interference withpolyadenylation in the context of either SV40 late polyA sequence orSV40 early polyA sequence, as shown in Example 4-6. Further, todemonstrate the aptamer-modulated U1 interference, thus target geneexpression was not limited to SV40 polyA sequences, we tested theguanine aptamer-modulated U1 interference in the context of the polyAsequence from human beta globin gene. As shown in FIG. 8, upon guaninetreatment, the luciferase activity increased 2.1 fold fromwtU1_Gua_HBGPA construct. In contrast, the mutU1_Gua_HBGPA didn't induceluciferase activity when comparing to the untreated samples. Theseresults demonstrate that aptamer-modulated U1 interference is not polyAsequence specific.

Listing of claims:
 1. A polynucleotide cassette for the regulation of the expression of a target gene comprising a riboswitch wherein the riboswitch comprises an effector region and an aptamer, wherein the effector region comprises a U1 snRNP binding site and sequence complementary to the U1 snRNP binding site.
 2. The polynucleotide cassette of claim 1, wherein the aptamer binds a small molecule ligand.
 3. The polynucleotide cassette of claim 1, wherein the effector sequence comprises additional sequence that is capable of forming a stem when the aptamer binds ligand.
 4. The polynucleotide cassette of claim 3, wherein the effector region comprises a stem-forming sequence that is 9 to 11 base pairs.
 5. The polynucleotide cassette of claim 4, wherein the effector region comprises a stem-forming sequence with one or more mismatched bases in the stem.
 6. The polynucleotide cassette according to claim 1, wherein the U1 snRNP binding site is 8 to 10 nucleotides.
 7. The polynucleotide cassette of claims according to claim 1, wherein the U1 snRNP binding site comprises the sequence CAGGTAAG.
 8. The polynucleotide cassette according to claim 1 wherein the U1 snRNP binding site is selected from the group consisting of CAGGTAAGTA, CAGGTAAGT, and CAGGTAAG.
 9. A polynucleotide cassette of claim 1, wherein the polynucleotide cassette comprises two or more riboswitches, wherein each riboswitch comprises an effector region and an aptamer, wherein the effector region comprises a U1 snRNP binding site and sequence complementary to the U1 snRNP binding site.
 10. The polynucleotide cassette of claim 9, wherein the two or more riboswitches each comprise an aptamer that binds the same ligand.
 11. The polynucleotide cassette of claim 9, wherein the two or more riboswitches comprise different aptamers that bind different ligands.
 12. A method of modulating the expression of a target gene comprising a. inserting one or more of the polynucleotide cassettes of claim 1 into the 3′ UTR of a target gene, b. introducing the target gene comprising the polynucleotide cassette into a cell, and c. exposing the cell to a ligand that specifically binds the aptamer in an amount effective to increase expression of the target gene.
 13. The method of claim 12, wherein the ligand is a small molecule.
 14. The method of claim 12, wherein the polynucleotide cassette is inserted about 87 or about 140 nucleotides 5′ of the polyadenylation signal.
 15. The method of claim 12, wherein the polynucleotide cassette is inserted about 74, about 110, or about 149 nucleotides 5′ of the polyadenylation signal.
 16. The method of claim 12, wherein two or more of polynucleotide cassettes are inserted into the 3′ UTR of the target gene.
 17. The method of claim 14, wherein the two or more polynucleotide cassettes comprise different aptamers that specifically bind to different small molecule ligands.
 18. The method of claim 14, wherein the two or more polynucleotide cassettes comprise the same aptamer.
 19. The method according to claim 16, wherein the two or more polynucleotide cassettes are inserted at different locations of the 3′ UTR of the target gene.
 20. The method according to claim 12, wherein the target gene comprising the polynucleotide cassette is incorporated in a vector for the expression of the target gene.
 21. The method of claim 20, wherein the vector is a viral vector.
 22. The method of claim 21, wherein the viral vector is selected from the group consisting of adenoviral vector, adeno-associated virus vector, and lentiviral vector.
 23. A vector comprising a target gene that contains a polynucleotide cassette of claim
 1. 24. The vector of claim 23, wherein the vector is a viral vector.
 25. The vector of claim 24, wherein the viral vector is selected from the group consisting of adenoviral vector, adeno-associated virus vector, and lentiviral vector. 